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Old Sep 11, 2012, 10:37 PM
The Prez....... again
kenh3497's Avatar
United States, IA, Rockwell
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Full flying stab. Good, Bad or Indifferent?

Excuse my newbness

I've not seen a DLG with a full flying stab. Like everything there are pitfall to each design. In my simple mind I would think a FFS would solve some problems, like decalage. Maybe it's to heavy??

Ken
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Old Sep 11, 2012, 10:52 PM
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FF Stab

Quote:
Originally Posted by kenh3497 View Post
Excuse my newbness

I've not seen a DLG with a full flying stab. Like everything there are pitfall to each design. In my simple mind I would think a FFS would solve some problems, like decalage. Maybe it's to heavy??

Ken
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Old Sep 11, 2012, 10:52 PM
G_T
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Full flying stabs have been used on a number of DLGs with very good results. The stab can generally be lighter and stronger, but the mount is not as easy. The aerodynamics of a full flying stab are better, but the drag of the stab mount is arguable. Some are pretty heavy and draggy. They can be light and fairly clean.

I slightly prefer full flying stabs on DLGs. YMMV. Either full flying or hinged can work very well.

http://www.rcgroups.com/forums/attac...mentid=3146678
http://www.rcbuilder.com/V-Mount-for...ider_p_32.html
http://www.hyperflight.co.uk/product...de=ELF-V-MOUNT
http://www.hyperflight.co.uk/getpic....code=BLASTER-3
http://shop.singahobby.com/?q=node/27997

These are just some pictures I grabbed. Full flying stabs are alive and well on DLGs. But they are in the minority.

Gerald
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Old Sep 11, 2012, 11:00 PM
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Hi Ken,

Welcome to this segment of the hobby. For me, a full flying stab is decidedly different to fly in a DLG versus a segmented or hinged stab, and not necessarily better or worse. I have a Stobel which I fly regularly (hinged stab), and have flown a Lightspeed and Blaster, each of which feature a FFS. Of course these are very different designs. I personally prefer the "feel" of a FFS (try one if you get a chance), but caution that the elevator linkage needs to be perfect. And I do mean perfect. A tiny bit of gear lash or slop in a hinged set up seems somewhat forgivable, but on the FFS it just won't cut it. As G_T stated, YMMV, but I would be aware of this weakness, which is design specific to me.
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Old Sep 11, 2012, 11:31 PM
Walter Roos
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Gerald,
I don't see why the Full Flying Stab would be " Stronger". It is more complicated and I have seen several of them fail at contests. In particular on the Blaster 3., which is why I went with a tail mount from the Taboo GT on my B3, using a hinged stab instead.

I admit I don't have any personal experience with other DLGs using the Full Flying stabs.

We probably need to ask Gavin as he would know which is stronger.

walt
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Old Sep 11, 2012, 11:51 PM
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I've had both and if I'm building my own mount I prefer the hinged stab (if I spent an hour making a simple mold for V-mounts that might change). If I'm not making it then it's kind of a toss up. I like string/spring setups, which are difficult to engineer with a full-flying. On the other hand, the things I like about a full flying is not having to worry about the AOA of the stab (though I admittedly have never really worried about it on a hinged, either) and the control authority I get at slow speeds. At the top of launch it seems like my B2 is much easier to push over without stalling first. My other planes are a bit more sluggish at that low speed and I have to push over a little sooner to avoid stalling. YMMV.

Brandon
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Old Sep 12, 2012, 08:48 AM
I'm slow but I'm expensive
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A stab without a hinge line cut into it is "intact". Imagine squashing a tube with and without a slice in it. Strength of the entire system, don't know.
Ken
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Old Sep 12, 2012, 08:53 AM
G_T
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No hingeline means no cuts across the fibers which means stronger for the same size and shape and thickness. This allows one to use a more optimal airfoil to lower drag somewhat. Drag is the enemy of our DLGs.

Walt, it sounds like the issues you are talking about are mount related, not full-flying per se. I'm not sure I'd even call it intrinsically all that more complex. However many mounts in use are certainly way more complex and way overweight compared to what one can do.

Were I making conventional mounts, I'd have to make stock strips of the stuff and cut them up (or else I'm spending too much time on each). I'd need hardpoints in the mount pieces for bolts or a bolt and a pin. I'd need hardpoints in the stab. I'd need a hinge, which means putting in hinge fabric or using Kevlar skins or using tape, and I'd have to cut the hinge.

Were I making Spring-V mounts, I'd have to make stock strips and cut them up. No hinge required. No hardpoints required on the stab in the conventional sense but a patch of glass should go in the mount area. That's quicker and easier than a hardpoint.

Both mount methods would need to be glued to the tailboom. Both methods need something to act as the control horn. Pushrods are best for full flying, but a light carbon pushrod is one of the lightest and stiffest systems anyway. Pull spring can be done for elevator, but it has its own hassles - stretch, increased thermal drift (run the numbers on the total expansion of your favorite system if you don't believe me). And one has to make and install a spring. Not much difference really IMHO.

Of course, if your fuselage comes with some mount on it, and it is where you want it, the easiest thing is to just use it!

Now a conventional V-mount is more complex than what I do. No question about that. I just consider it completely unnecessary at our size range and it introduces an extra level of slop due to the stab bolting onto the mount's support plate.

As to the comment on slop - it is unacceptable on an elevator linkage, regardless of elevator type. It makes a difference.

Gerald
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Old Sep 12, 2012, 09:41 AM
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Full flying = very good but a bit of a pain mechanically

If I'm building one or two airplanes for me, I build full flying.

For production work... no brainer... hinged.
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Old Sep 12, 2012, 11:52 AM
Time for me to Fly...
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I liked the full flying stab on my B3. It takes the guess work out of trimming the angle of declage. Just trim the plane in flight and forget about it. I think id want a pushrod there instead of a spring, however. There is a lot more surface to have to hold with a full flying stab. RC Builder offers a V mount but I've never used it. Maybe I should give one a try sometime. Humm.... Do the Fr3aK stabs work well for a full flying setup?
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Old Sep 12, 2012, 12:33 PM
The Prez....... again
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Thanks for the insite! In the power world, you just don't see FFS all that much. I have seen a pattern ship or two with it but there is a "bunch" of mechanical linkage that would be much to heavy even if scaled down.

A good picture in post #19 here. http://www.rcgroups.com/forums/showt...ht=flying+fork

Ken
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Old Sep 12, 2012, 12:51 PM
Time for me to Fly...
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You saw the one that RC Builder offers, right? If not, here it is.
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Old Sep 12, 2012, 12:56 PM
The Prez....... again
kenh3497's Avatar
United States, IA, Rockwell
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Quote:
Originally Posted by Mr. Wiz View Post
You saw the one that RC Builder offers, right? If not, here it is.
I did now Very nice piece of hardware. It is kind of what I envisioned, but wasn't quite sure how it would be constructed.

Ken
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Old Sep 12, 2012, 12:59 PM
Aurora Builder
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Why I am responding to yet another horizontal tail thread I know not...

The v1 Fr3aK tails use Freak V2 airfoils that are not optimized for full flying. They will work OK but the Edge Horizontal v2 is better. Still, I think decalage is a very minor point, please read Drela's comments on the subject.

In the power world, and frankly even the DLG/glider world, full flying is higher risk than a conventionally mounted tail. I agree with Gerald on all his points w.r.t to DLG's, but he fails to address one point, and that is linkage failure. It is bad in both tail arrangements but worse in full flying. If the full flying linkage and/or mount setup breaks, its pretty much a guarantee to end very badly. If you do the same on a fixed stab+elevator, it is less likely for the mount to fail mechanically, as usually 2 bolts hold it in place and more contact area is available to glue it to the boom. If the linkage fails, its definitely not good but your plane doesn't instantly become an unstable lawn dart, the fixed part still provides some stability and may let you fly the plane using camber control to the ground.

Under higher load situations, i.e powered aircraft, full flying failure can be deadly. The engineering is more complex, and the parts heavier under such load cases than a fixed stab. The advantage is you have a larger c.g range, which is why some commercial aircraft have them (Boeing 737 for example).
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Old Sep 12, 2012, 01:19 PM
Time for me to Fly...
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If you are using a spring setup on any type of elevator and the linkage fails it's going to end badly. Probably the same for the spring setup on a rudder too but maybe not. If you can manage to flatten out the turn with opposite aileron. You'd have to be awfully darn quick in your assessment of what actually happened though to have even that slim chance of it working out.

All that said, I think I'll stick with simple based on your comments, Sam.
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